The Hellhound has a series of attacks
- grow ice antlers and sweep at you when in range
- pound the ground and unleash earth magic
- stop and breathe fire
The best way to deal with it is hit & run tactics. Run forward, use the chains (D-pad right) to do long range hits and then right stick to dodge away.
There are blue and red masks in the arena you fight the Hellhound, lure it towards the cliff edge and then dodge back to give yourself time to pick them up.